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value of the fuel under good practice to 49 per cent, or more under bad practice. One-third of this loss is due to the excess air, it being assumed that twice the necessary amount is used. The dif-
TABLE II-H. Loss of Heat in Products of Combustion.
Temperature of waste gas. Degrees Fahr.	Heat loss ; per cent, of fuel value.		Heat utilized ; per cent, of fuel value.	Proportionate fuel needed.
	By excess air.	Total.		
500 800 1100 1400	7 11 15 19	22 36 49 03	78 64: 51 37	100 122 153 311
ference between good and bad practice is 27 per cent, or just about one-quarter of the total value of the fuel. A boiler forced beyond its capacity so that the escaping gases are at a temperature of 1100° F. will need 53 per cent, more fuel than one where the gases are at 500° F. If the stack is red hot, as is sometimes the case, the boiler is using twice as much fuel as is needed under good conditions.
SEC. lit.—Use of tunnel head gas for the production of power T)y steam engines.—It has been shown that a boiler under good conditions loses in the stack gases from 20 to 30 per cent, of all the energy in the fuel. There are other losses, as, for instance, by radiation, so that the average modern boiler plant running on furnace gas will probably not give over 60 per cent, efficiency. It has also been proven that the tunnel head gas from one ton of coke contains energy equivalent to 16,000,000 B.t.u. and that the stoves require 5,000,000 B.t.u., leaving 11,000,000 B.t.u. for the production of power. In a furnace using 400 tons of coke per day the amount available would be 4,400,000,000 B.t.u. per day. The pumps and hoisting engines require, say, 300 B.h.-p., or a total of 240,000,000 B.t.u. in the form of steam. Assuming 60 per cent, efficiency in the boiler plant, this represents 400,000,000 B.t.u. in the gas, which, being subtracted from 4,400,000,000, leaves 4,000,000,000 B.tu. for the blowing engine and other purposes. A good engine requires about 9-16 of one boiler horse-power to produce an indicated horse-